It known that a cooling system basically comprises a compressor, a condenser, an expansion device and an evaporator. The refrigerant (in its gaseous phase) is compressed in the compressor and flows to the condenser, where it is cooled, for example, by the air, and passes to the liquid phase. The refrigerant in high pressure, flows to the expansion device, where its pressure is reduced, and then flows to the evaporator and absorbs heat from the load (for example, food) and passes into the gas phase. Finally, the refrigerant is sucked by the compressor, thus completing the refrigeration cycle.
It is known various types of refrigeration systems of household refrigerators. The most commonly used cooling systems comprise a compressor and a condenser, from where a refrigerant line leaves to the evaporator of the freezer, and then this line passes through the evaporator of the refrigeration compartment and returns to the compressor.
Although the system described above has lower costs, it is inefficient since it operates at lower temperatures, i.e. at the temperature of the freezer.
In other cooling systems of the prior art there are two completely independent systems, one operating in the freezer and the other operating in the refrigeration compartment. This configuration provides a good efficiency, although its cost is very high, since it has two compressors and two capacitors.
An alternative to these cooling systems is described in document U.S. Pat. No. 5,531,078, which discloses a system especially suitable for use in a dual evaporator refrigeration cycle (having at least two independent climate chambers). This system uses only one fluid compressor provided with a single suction inlet and a single pressured outlet. The suction inlet is supplied by a suction system that consists of a single main suction line, which comes from the junction of two intermediate suction lines. The above suction lines are also known as return lines (thus, the suction system described in document U.S. Pat. No. 5,531,078 provides two intermediate return lines and a return final line).
The cooling system described in document U.S. Pat. No. 5,531,078 is best illustrated in FIG. 1, wherein it becomes possible to verify that the union of the two intermediate suction lines “LIS1” and “LIS2” occurs with the aid of a one-way valve “VU” resulting in a single main suction line “LPS”, which is connected to the suction inlet “ES” of the compressor “C”. Also according to FIG. 1, it can be verified that at least one of the two intermediate suction lines “LIS1” or “LIS2” has a check valve (on-off) “VB”.
The operation of the suction system of the refrigeration system described in document U.S. Pat. No. 5,531,078 is simple: the intermediate suction line “LIS1” of higher pressure (which has a check-valve “VB”) supplies the main suction line “LPS”, which supplies the compressor “C”. Currently, the unidirectional valve “VU” prevents the pressure in the intermediate suction line “LIS1” to invade the intermediate suction line “LIS2”, which has a lower pressure. Therefore, the compressor C is supplied with “high pressure”. When the check-calve “VB” interrupts the pressure of the intermediate suction line “LIS1”, the low pressure of the main suction line “LIS2” flows through the unidirectional valve “VU” to the main suction line “LPS”, and consequently, to the compressor “C”. This type of suction system allows that a single compressor with a single suction inlet to be capable of working with two different pressures. This also allows the compressor “C” to work at high and low pressures in alternating cycles, optimizing its energy ratio (compared to other arrangements existing in the state of the art).
However, the suction system of the refrigeration system described in document U.S. Pat. No. 5,531,078 has a major drawback: the occurrence of parasite volume of high pressure/low pressure in the beginning of the low pressure/high pressure cycles. This parasite volume occurs mainly by the fact that when the check valve “VB” is actuated (which occurs when it is desired to alternate the cycles of high and low pressure), the intermediate suction line LIS1 or the main suction line “LPS” is pressurized with the pressure opposite to the desired working pressure. That is, upon alternating from high pressure to low pressure, the intermediate suction line “LIS1” remains pressurized, and, therefore, part of the cycle to be supplied at low pressure is still being supplied at high pressure. Moreover, upon alternating from low pressure to high pressure, the main suction line “LPS” remains pressurized at low pressure, and, therefore, part of the cycle to be supplied at high pressure is still being supplied at low pressure. This negative feature is inadmissible in application where the cycles alternating rate (high pressure and low pressure) is high and not fixed, since the occurrence of parasite volume at high pressure/low pressure will be constant.
It can also be observed that, more broadly and generally speaking, another drawback of all systems of the prior art consists in the fact that they always operate within temperature ranges, i.e., when the temperature reaches a preset maximum value, the thermostat sends a signal to stop the compressor operation or reduces its rotation (in the case of variable capacity compressors), and when the temperature reaches the lowest value, the system returns to operating at full capacity. These variations also cause high losses.